1. Field of the invention
The present invention relates to a waste gas treatment apparatus.
2. Description of the Related Art
In a conventional waste gas treatment apparatus, a catalyst forming a moving layer is accommodated between two parallel louvers. The catalyst is caused to move downward in a vertical direction, while a gas to be treated is fed into the moving layer through one louver, and the treated gas is discharged through the other louver.
FIG. 1 is a schematic view of a conventional waste gas treatment apparatus.
In FIG. 1, reference numeral 31 denotes a tower, wherein a gas inlet 34 and a treated gas outlet 35 are formed on opposed side walls 32 and 33, respectively. The interior of the tower 31 is partitioned by an inlet louver 11 and an outlet louver 12 which are disposed in parallel with each other. An unillustrated catalyst is accommodated between the inlet louver 11 and the outlet louver 12 to thereby form a moving layer 10.
A gas to be treated is fed into the moving layer 10 through the gas inlet 34 and the inlet louver 11. The fed gas sufficiently contacts the catalyst in the moving layer 10, so that dust is collected, and the gas is desulfurized and denitrated. The thus-treated gas is discharged from the treated gas outlet 35, through the outlet louver 12.
Meanwhile, the catalyst is fed into the moving layer 10 through a feed port 46 formed at the top end of the tower 31, moves downward in the moving layer 10, and is discharged through a discharge port 16.
A discharge roller 18 is disposed at the discharge port 16 and is rotated in the direction of the arrow at a predetermined speed, so that the catalyst moves downward in the moving layer 10 at a predetermined speed and is discharged through the discharge port 16.
The catalyst discharged through the discharge port 16 circulates to the feed port 46 through a regeneration apparatus 60 and a line 61. Reference numerals 13 and 14 denote lower walls, and numeral 20 denotes a flow-straightening cone.
FIG. 2 is a sectional view of essential portions of the conventional waste gas treatment apparatus.
As shown in FIG. 2, a catalyst 19 is accommodated in a space defined by the inlet louver 11 and the outlet louver 12 disposed in parallel with each other, to thereby confine the moving layer 10. The lower walls 13 and 14 extend obliquely downward from the bottom ends of the inlet and outlet louvers 11 and 12, respectively. The distance between the lower walls 13 and 14 gradually becomes narrower in the downward direction, to thereby form the discharge port 16 at the bottom ends of the lower walls 13 and 14. The discharge roller 18 is disposed at the discharge port 16. The flow-straightening cone 20 having an inverted-V-shaped cross section is disposed along the discharge port 16 in the lower area of the moving layer 10 so as to smoothly direct the catalyst 19 downward.
However, in the aforementioned conventional waste gas treatment apparatus, the form of the catalyst 19 changes from pattern a to pattern b as it moves downward in the moving layer 10.
In this case, the catalyst 19 fails to uniformly move in the moving layer 10 and moves at a slower speed in the vicinity of the inlet louver 11. Accordingly, in the vicinity of the inlet louver 11, the catalyst 19 becomes clogged with dust which is contained in the incoming gas. Also, the catalyst 19 stagnates in a boundary area c between the inlet louver 11 and the lower wall 13, a boundary area d between the outlet louver 12 and the lower wall 14, and a top surface e of the flow-straightening cone 20.
In order to prevent the catalyst 19 from becoming clogged with dust and from stagnating, there is provided a waste gas treatment apparatus (refer to Japanese Patent Application Laid-Open (Kokai) No. 7-136445) wherein the space of the moving layer 10 is divided into a front chamber and a rear chamber by a perforated plate such that the catalyst 19 in the front chamber moves at a sufficiently higher speed than does the catalyst 19 in the rear chamber.
However, in such a waste gas treatment apparatus, an increased moving speed of the catalyst 19 in the front chamber causes the catalyst 19 to form a powder due to wear and causes the thus-formed powder to scatter. Thus, dust concentration at the treated gas outlet 35 (FIG. 1) increases accordingly, resulting in failure to reduce dust in a flue gas discharged from an unillustrated stack to an insignificant level (5 to 10 mg/Nm.sup.3).
If the moving speed of the catalyst 19 in the front chamber is limited, the desulfurizing efficiency and denitrating efficiency of the catalyst 19 decrease accordingly.